(1) Technical Field
This invention relates to electronic circuits, and more particularly to multi-state attenuator circuits.
(2) Background
An attenuator is an electronic device that reduces the power of a signal without appreciably distorting its waveform. An attenuator is functionally the opposite of an amplifier (although the two work by different methods)—while an amplifier provides gain, an attenuator provides loss (or, equivalently, a gain less than one). Classic examples of radio frequency (RF) attenuators are bridged-T type, pi-type, T-type, and L-pad type attenuators.
A multi-state attenuator may be formed with switched resistive elements for varying the circuit configuration and attenuation values. An example of one type of multi-state attenuator is shown in U.S. Pat. No. 5,157,323, entitled “Switched Low-Loss Attenuator”, issued Oct. 20, 1992 to Ali et al.
It appears that the circuit design taught in the '323 patent essentially teaches a signal line with IN and OUT terminals coupled to multiple parallel shunt circuits and to multiple parallel attenuation circuits (see FIGS. 1 and 2 of the '323 patent). It appears that any of the multiple parallel shunt circuits can be activated at a particular time, as can any of the multiple parallel attenuation circuits.
One benefit of the circuit taught in the '323 patent is that a single composite structure defines all of the attenuation states, thereby reducing the cumulative insertion loss required in conventional series-connected “cascaded” design approaches. However, a drawback of the circuit type taught in the '323 patent is that it does not provide for handling of high power signals, or provide flexibility of design for various applications.
The present invention is addresses these limitations.